1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, a liquid crystal display device with a built-in touch screen, which facilitates to improve display quality and to reduce a manufacturing cost by a simplified manufacturing process, and a method for manufacturing the same.
2. Discussion of the Related Art
With the developments in various mobile electronic equipment, such as mobile terminals and notebook computers, there is the increasing demand for an applicable flat panel display device.
The flat panel display device may include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display device (FED), a light-emitting diode display device (LED), etc.
Among the various flat panel display devices, the LCD device is widely used owing to various advantages. For example, technical developments have been made for the mass production of LCD devices, the driving means is easy, power consumption is low, and the LCD devices have high-quality resolution and large-sized screens.
Instead of using a related art mouse or keyboard as an input device of the flat panel display device, a touch screen is used as a new input device for the flat panel display device, wherein the touch screen enables a user to directly input information by the use of finger or pen.
The touch screen has been widely applied in various fields, for example, mobile terminals such as navigation, terminal for industrial use, notebook computer, automatic teller machine (ATM), mobile phone, MP3, PDA, PMP, PSP, mobile game machine, DMB receiver, and tablet PC; and electric appliances such as refrigerator, microwave oven, and washing machine. Furthermore, the easy operation of the touch screen rapidly enlarges the application field.
On application of touch screen to the LCD device, an LCD device with a built-in touch screen has been researched and developed to achieve a slim device.
FIG. 1 illustrates an LCD device with a built-in touch screen according to the related art, and a method for driving the same.
Referring to FIG. 1, the LCD device with a built-in touch screen according to the related art comprises lower and upper substrates 50 and 60 bonded to each other with a liquid crystal layer (not shown) interposed therebetween.
On the upper substrate 60, there are a black matrix 62; red, green, and blue color filters 64R, 64G, and 64B; and an overcoat layer 66. In this case, the black matrix 62 defines a pixel region corresponding to each of plural pixels. Also, the red, green, and blue color filters 64R, 64G, and 64B are respectively formed in the respective pixel regions defined by the black matrix 62. The overcoat layer 66 covers the red, green, and blue color filters 64R, 64G, and 64B and the black matrix 62, to thereby planarize the upper substrate 60.
On the lower substrate 50, there is a pixel array 40 including plural pixels to drive the liquid crystal layer and detect a touching point by finger or pen.
Each of the plural pixels is defined by gate and data lines crossing each other. At the crossing portion of the gate and data lines, there is a thin film transistor (hereinafter, referred to as ‘TFT’). Each of the plural pixels includes a common electrode and a pixel electrode.
Recently, an in-cell touch type LCD device has been researched and developed, wherein the in-cell touch type LCD device refers to an LCD device that uses an element existing in the related art structure as a touch-sensing electrode (for example, a common electrode Vcom may be used as a touch-sensing electrode).
FIG. 2 is a cross section view illustrating a lower substrate in the LCD device with a built-in touch screen according to the related art. FIG. 2 shows a common electrode formed in the X-axis direction among all common electrodes of the LCD device.
In the LCD device with a built-in touch screen according to the related art, as shown in FIG. 2, a common electrode 75 of a lower substrate 50 not only supplies a common voltage (Vcom), but also functions as a sensing electrode for detection a user's touch.
For detection of the user's touch, the common electrodes (sensing electrode) 75 are formed in the X-axis and Y-axis directions. The common electrode 75 in the X-axis direction is brought into contact with a gate metal 73 at a lower portion of the lower substrate 50 through a contact structure, to be described.
In more detail, each pixel of the lower substrate 50 includes a buffer layer 51 on a glass substrate; a gate insulating layer 52; the gate metal 73; an interlayer dielectric (ILD) 53; a contact metal 74; a first passivation layer (PAS0) 54; a second passivation layer (PAS1) 55; the common electrode (Vcom) 75; a conductive line (3rd metal) 76; a third passivation layer (PAS2) 56; and a contact electrode 77.
The first to third passivation layers (PAS0 to PAS2) 54 to 56 are partially etched to thereby form a contact hole for exposing a predetermined portion of the contact metal 74.
In addition, the third passivation layer (PAS2) 56 is additionally etched to expose the conductive line 76.
The gate metal 73 is formed of metal used for forming gate line.
The contact metal 74 is formed of metal used for forming source and drain electrodes of TFT.
The contact electrode 77 is formed of a transparent conductive material used for a pixel electrode (for example, ITO). Also, the contact electrode 77 is formed simultaneously with the pixel electrode.
According as the first, second, and third passivation layers 54, 55, and 56 are partially etched, the contact hole for exposing the contact metal 74 is formed in the contact electrode 77. Also, the conductive line 76 is exposed by etching the third passivation layer 56 thereabove.
The contact electrode 77 is formed inside the contact hole and simultaneously on the third passivation layer (PAS2) 56. Thus, the contact electrode 77 is electrically connected with the contact metal 74 and the conductive line 76.
Through the contact structure between the contact electrode 77 and the contact metal 74, among the entire common electrodes driven as the touch-sensing electrode, the common electrode 75 in the X-axis direction is brought into contact with the gate metal 73.
For bringing the common electrode 75 in the X-axis direction into contact with the gate metal 73 in the in-cell touch type LCD device according to the related art, the contact electrode 77 is formed simultaneously with the pixel electrode.
If the common electrode 75 is brought into contact with the gate metal 73 by the use of transparent metal for the pixel electrode, an aperture ratio of the corresponding pixel with the contact structure is relatively lower than that of the other pixels.
In order to connect the common electrodes of the neighboring pixels in the X-axis direction in the related art contact structure, the conductive line 76 is connected with the contact electrode 77, and the contact metal 74 connected with the gate metal 73 is connected with the contact electrode 77. This double contact structure may cause the structural problem of the increased size of the contact portion.
The aperture ratio in the pixel with the contact structure is lowered by the increased size of the contact portion. Especially, in case of the pixel structure with plural domains, the contact structure using the transparent metal of the pixel electrode is used so that an aperture ratio of the corresponding pixel is about 80% as compared to that of the neighboring pixels.
Accordingly, the pixel with the contact structure may be shown as a dark point when a viewer watches the corresponding pixel with the contact structure, to thereby lower visibility. As a result, a picture quality of the LCD device is deteriorated. The double contact structure may cause the complicated manufacturing process and low manufacturing efficiency.